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 <h1>Stream Filters</h1>

 <p class="simpara">
  A <code class="literal">filter</code> is a final piece of code which may perform
  operations on data as it is being read from or written to a stream.
  Any number of filters may be stacked onto a stream. Custom
  filters can be defined in a PHP script using
  <span class="function"><a href="function.stream-filter-register.html" class="function">stream_filter_register()</a></span> or in an extension.
  To access the list of currently 
  registered filters, use <span class="function"><a href="function.stream-get-filters.html" class="function">stream_get_filters()</a></span>.
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